Various systems and methods are known in the art for assaying unidentified radionuclides to provide a qualitative and/or quantitative estimate of the source and/or type of the radioactive material present. For example, radionuclides naturally decay according to known and predictable decay chains that produce one or more isotopes until eventually a stable isotope is reached, and each decay generates alpha, beta, and/or gamma emissions. The alpha, beta, and/or gamma emissions may be measured to determine the specific radionuclides present in a sample. For example, the energy levels and/or timing of the alpha, beta, and/or gamma emissions may be measured to identify each radionuclide producing the emissions, and the ratio of the specific radionuclides present in the sample may then be used to identify the source and/or type of the radioactive material present.
For many of the radionuclides of interest, however, beta emissions are characterized by a broad energy continuum and alpha emissions by extremely short ranges. Their assay typically requires extensive chemical purification of the elements of interest and preparation of an extremely thin deposit of the activity prior to measurement. This is particularly true of alpha emitting actinide isotopes. It may be problematical to accomplish the measurement of these alpha emitters in a timely manner in a sample with a complex mixture of beta and gamma-ray activities such as “fresh” fission products. In addition, low energy gamma emissions are difficult to distinguish from other Compton scattering events. Therefore, an improved system and method for assaying alpha emitting radionuclides in a high beta/gamma background environment would be useful.